One of such conventional systems has the following construction: A pair of opposed posts with horizontal rectangular cross sections each have a vertically movable carriage connected thereto for vertical movement. The carriage is provided with an arms installing section. The installing section of each carriage projects toward the installing section of the other carriage. In other words, the installing sections are located on the respective opposed sides of the two posts. A pair of horizontal swing arms are connected, at their inner ends, to vertical pivots provided at opposed ends of each installing section. A lock gear is connected to the inner end of each swing arm. The lock gear has an arcuate toothed wall which is concentric with the pivot installing the arm. A common vertical rod is provided in conjunction with the lock gears connected to the two arms. The vertical rod is connected to the carriage, and is vertically movable. The swing arms are unfixed, in their horizontal positions, by the vertical rod coming into contact with a base. The lock gear and the vertical rod are connected to each other, by means of a link, on an upper surface of the installing section.
In such a conventional construction, since the arms installing sections project toward each other and the links are exposed on the upper surfaces of the installing sections, these sections and the links may prevent doors of an automobile lifted by the arms from being opened wide for repair of the inside of the automobile. Also, since the link is located straight between the inner ends of the arms, a lever for manually unfixing the arms must be connected to the link at the central portion of the arms installing section. Thus, it is not easy to operate the lever.